1. Field of the Invention
The present invention relates to a manipulator, a manipulator collision detecting method and a manipulator control method.
2. Description of the Related Art
In recent years, robots are making inroads into not only industrial fields, but also service fields such as medicine, welfare and household chores. Robots used in such places share operation spaces with people. Thus, there is no other choice to presume interferences of people and robots such as contacts and collisions in such environments and it is important to ensure safety against these.
Conventional manipulators represented by industrial manipulators are each constructed by combining a highly rigid member and a highly rigid actuator (such as a motor using a gear having a high speed reduction ratio) in order to ensure the accuracy of a tip position (see, for example, Japanese Examined Utility Model H04-29990B).
Thus, if an external object such as a person or a structure suddenly goes into a planned trajectory of a manipulator to come into contact with the manipulator, it is difficult to instantaneously relieve its impact force and contact force. This is because the manipulator has a non-backdrivable mechanism. Accordingly, improvement is necessary in ensuring safety for humans. Various technologies have been proposed to ensure safety against contact with an external object in such manipulators.
For example, there has been disclosed technology for detecting the collision or contact of the tip of a manipulator with an external object such as a person or a structure using a force sensor disposed at a manipulator wrist and position-controlling motors for joints of the manipulator according to an inputted force (magnitude, direction) to realize spring-like flexibility by way of a control (see, for example, Japanese Unexamined Patent Publication No. H02-300808).
However, the above manipulator has a problem of being unable to react to collision and contact with parts of the manipulator other than the tip portion.
Further, in the manipulator of Japanese Unexamined Patent Publication No. H02-300808, a pressure sensor or the like is provided on the outer surface of the manipulator so as to be able to detect a collision or contact with the parts of the manipulator other than the tip portion. However, there is a limit in response to collisions since the motors are controlled based on a sensor input. Such a sensor input has a high possibility of malfunction due to electromagnetic waves and the like and presents a problem that a reliable operation cannot be expected.
Furthermore, the special sensor as described above is necessary to detect a collision, which causes malfunctions resulting from the breakage of sensor wiring, a weight increase and a cost increase of the manipulator.